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The Effects of Surface Topography and Lack of Fusion on the Fatigue Strength of Laser Hybrid WeldsAuthors:Md. Minhaj Alam, Lulea University of Technology; Lule� SwedenZuheir Barsoum, Royal Institute of Technology (KTH); Stockholm SwedenPer Jonsen, Lulea University of Technology; Lulea SwedenHans Ake Haggblad, Lulea University of Technology; Lulea SwedenAlexander Kaplan, Lulea University of Technology; Lulea SwedenPresented at ICALEO 2009

The geometrical aspects of laser hybrid welding before, during and after the process differ from autonomous laser welding and from arc welding. When studying the fatigue behaviour of laser hybrid welded fillet joints we identified that the microgeometry, i.e. the surface ripples can be more critical than the macrogeometry of the weld surface and even than lack of fusion (LOF), which frequently was detected. The plastic replica method was applied to measure the toe radii at the weld edges while the topography was identified by interferometric profilometry. From metallurgical analysis of the joint interface the tendency to LOF can be explained. Stress analysis was carried out by FEA for the complex joint geometry and bending load situation, showing maximum stress on the weld toes, even when including LOF. It was shown that the position and value of the maximum stress depends on a non-trivial combination of the weld geometry, including possible LOF, and the surface topography. Thus it can be explained that at compressive stress conditions LOF does not contribute significantly to the fatigue strength of laser hybrid welds while the surface topography does. Recommendations for defining and in turn avoiding critical geometrical aspects during the welding process are discussed.

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